1. Field of the Invention
The present invention relates to an airbag deployment controller which drives an airbag unit with use of a main sensor and a sub sensor as well as a passenger protection device including such an airbag deployment controller.
2. Description of the Related Art
In the prior art, a motor vehicle comprises a passenger protection device having an airbag. For example, Japanese Unexamined Patent Application Publication No. 2006-44432 discloses a passenger protection device which comprises an airbag deployment determining unit, an airbag drive unit, and an airbag unit to drive the airbag drive unit for an airbag deployment when the airbag deployment determining unit determines to deploy the airbag according to detected values of a front acceleration sensor and a central acceleration sensor.
However, there is a drawback in the passenger protection device in that the airbag deployment determining unit may erroneously (falsely) determine to deploy the airbag when the front acceleration sensor and central acceleration sensor receive noises. For the purpose of preventing erroneous determination, a passenger protection device 101 as shown in FIG. 10 has been proposed.
The passenger protection device 101 comprises a front acceleration sensor 102, a central acceleration sensor 103, and a mechanical safing sensor 104. The front acceleration sensor 102 and the central acceleration sensor 103 constitute a main sensor while the mechanical safing sensor 104 constitutes a sub sensor.
In an airbag deployment controller 105 of the passenger protection device 101, a frontal collision logic 151 determines whether or not to deploy an airbag according to a detected value of the front acceleration sensor 102. Also, a central collision logic 152 determines whether or not to deploy an airbag according to a detected value of the central acceleration sensor 103.
In the airbag deployment controller 105, an OR circuit block 154 generates a drive signal for an airbag unit 106, upon receiving a determination to deploy the airbag from either the frontal collision logic 151 or the central collision logic 152.
Further, the airbag deployment controller 105 comprises a mechanical safing sensor block 153 which determines a turning-on/off state of the mechanical safing sensor 104. Specifically, as shown in FIG. 11, at an occurrence a of collision of a vehicle, an impact S applied to the mechanical safing sensor 104 causes a magnet 141 to move in an opposite direction to an impact direction, easing a spring force of a spring 142 to open a reed contact 143. From the open reed contact 143, the mechanical safing sensor block 153 determines that the mechanical safing sensor 104 is in an ON state, and inputs a result of the determination to an AND circuit block 155.
The AND circuit block 155 outputs a drive signal to the airbag unit 106 to deploy an airbag unit 106 when the mechanical safing sensor 104 is in the ON state as well as when the OR circuit block 154 determines to deploy the airbag. Then, the airbag unit 106 deploys the airbag.
That is, even when noises are inputted to the front acceleration sensor 102 and the central acceleration sensor 103, the AND circuit block 155 is prevented from outputting a drive signal to the airbag unit 106 since the reed contact 143 of the mechanical safing sensor 104 does not open. As described above, using the mechanical safing sensor 104, the passenger protection device 101 can prevent an erroneous operation of the airbag.
However, there still remains a problem in the mechanical safing sensor 104 that at an occurrence of collision, the mechanical safing sensor 104 is affected by a force from a direction different from the impact direction. Because of this, the reed contact 143 takes a lot of time to open. This causes a delay in determining to deploy the airbag, delaying deployment of the airbag. Without the mechanical safing sensor 104, erroneous operation of the airbag due to noises cannot be prevented with use of the electric sensors alone.